The present invention relates to a fuel tank, particular relates to an external fuel vapor emission adjusting device for adjusting the pressure of fuel vapor therein and stopping overflowing of fuel.
In the conventional technology, for avoiding the leaking of the fuel vapor in the fuel tank, a canister is applied at the passage connected with the atmosphere environment. The canister has a plurality of trap valves (filter) and activated carbons for trapping the hazardous substance in the fuel vapor and avoiding discharging it into the atmosphere and avoiding contaminating the atmosphere.
In addition, except that the fuel in the fuel tank is applied to the engine, the fuel vapor is also stored and purged to an engine air inlet connected to a recycling vent of the canister upon an intermittent negative pressure produced when the engine operates.
However, only one canister is generally provided, the filter capacity of the canister is limited by the quantity of the trap valve and activated carbon. For resolving this problem, a typical method for increasing the filter capacity is increasing the quantity of the trap valve and activated carbon, and adding the size and capacity of the canister.
In addition, the fuel vapor recycling is also limited by the quantity of the trap valve and activated carbon, i.e. the quantity of the trap valve and activated carbon needs to be determined according to the engine air displacement. Thus, the added trap valve and activated carbon brings resistance to the intermittent negative pressure of the engine, which obstructs the recycling of the fuel vapor.